Field of the Invention
The invention relates to a method for operating a Coriolis mass flowmeter having at least one measuring tube, at least one oscillation generator, at least one oscillation sensor and at least one strain sensor, wherein the oscillation generator is actuated with an oscillation excitation signal and the measuring tube is excited to oscillation by the oscillation generator, wherein the oscillation of the measuring tube is detected by the oscillation sensor and an oscillation sensor signal is generated, and wherein the strain sensor is mechanically coupled to the measuring tube via a connection.
Description of Related Art
Furthermore, the invention relates to a Coriolis mass flowmeter having at least one measuring tube, at least one oscillation generator, at least one oscillation sensor, at least one strain sensor and an evaluation unit, wherein the oscillation generator is designed to excite the measuring tube to oscillation, wherein the oscillation sensor is designed to detect the oscillation of the measuring tube and to generate an oscillation sensor signal, wherein the strain sensor is mechanically coupled to the measuring tube via a connection and wherein the evaluation unit is designed to generate an oscillation excitation signal and to actuate the oscillation generator with the oscillation excitation signal.
The functional principle of the Coriolis mass flowmeter is that the measuring tube having medium flowing through it is excited to oscillation by the oscillation generator, wherein the direction of oscillation of the measuring tube, and thus also the medium flowing in the measuring tube, has at least one component orthogonal to the direction of flow of the medium in the measuring tube. The orthogonal component of the oscillation of the medium flowing in the measuring tube evokes a Coriolis inertia force in the flowing medium that counteracts the orthogonal component of the oscillation. The Coriolis inertia force causes a phase difference to occur along the longitudinal axis of the measuring tube at two different locations on the measuring tube between the oscillations of the measuring tube, the phase difference being proportional to the mass flow of the medium through the measuring tube. The Coriolis mass flowmeter measures the phase difference and determines the mass flow of the medium from it.
The strain sensor is a sensor that measures the strain of its sensor body. In order for the strain sensor to measure a strain of the measuring tube, the sensor body has to be mechanically coupled to the measuring tube via the connection so that a strain of the measuring tube is transferred to the sensor body.
Generic Coriolis mass flowmeters are known from practice, in which the mechanical coupling is changed by the connections. The changes of the mechanical coupling via the connections can have different causes. Possible causes are aging or fatigue of the connections or external influences on the connections. The changes of the mechanical coupling via the connection causes the strain measured by the strain sensor to no longer correspond to the strain of the measuring tube and, consequently, the measuring strain is inflicted with error. It is not known from the prior art how the change of the mechanical coupling is determined.